Is It Crabgrass or Quackgrass in Your Lawn?

Coarse, weedy, wide-bladed grass whose appearance mars the uniform texture of lawngrass is often all mistakenly referred to as crabgrass. Crabgrass preventer is widely sold in springtime at national chains, hardware stores and garden centers.

Here’s the problem: crabgrass preventer controls crabgrass, when actually much of the weedy, wide-bladed grass in our lawns is quackgrass or tall fescue.  And crabgrass preventer has no effect on either of these. If crabgrass preventer products aren’t working to rid the lawn of wide-bladed grassy weeds, it’s possible it’s not crabgrass. Nine times out of ten, when I’ve looked at coarse, grass-type weeds that have been called “crabgrass,” they’ve turned out to be quackgrass or tall fescue.

How can we tell the difference between crabgrass and quackgrass?

• Crabgrass is an annual, which must grow each year from seed that sprouts in spring, grows during summer and then dies over winter. Quackgrass is a perennial, living year to year, growing back each spring from a winter-hardy roots system.
• Because crabgrass seed doesn’t germinate until soil temperatures warm above 50 degrees F. in spring, crabgrass plants don’t appear in the lawn until the seed germinates and a seedling has had time to grow and develop. Crabgrass might not be evident until late May or even June. Quackgrass, being a perennial, begins to grow from its established root system earlier in spring, usually growing about the same time that regular lawngrass begins to green and grow in early May.
• Both crabgrass and quackgrass are wide-bladed grasses, but an easy way to diagnose is to look closely at the leaf blades. Quackgrass has what are termed “clasping auricles,” which are easily seen at the point where the grass blade wraps around the lower stem. Crabgrass lacks these auricles.

  

  

  

  Crabgrass’s growth habit is noticeably “prostrate,” where the grass blades tend to lay more horizontally, giving the plant a squashed look. Quackgrass habit is upright.

  

  

  

• Crabgrass roots stay in a bunch. Quackgrass has very pronounced white/tan rhizomes that run horizontally underground, spreading the plant. Digging a plant is an easy way to identify between crabgrass and quackgrass. Crabgrass is easier to pull out, roots and all.

  

  

  

• If allowed to go to seed and mowing doesn’t cut off the seedheads, crabgrass has a distinctive “goosefoot-shaped” seed head, while quackgrass has a straight seedstalk.

  

  

• Crabgrass is killed and turns brown about the time of fall frosts. Quackgrass remains green late into fall.
• Crabgrass seed can be prevented from germination if crabgrass preventer is applied before soil temperatures reach 57 to 60 degrees. Each year varies, but products can be applied in late April most years. There are “post-emergent” crabgrass killers that can be applied if the seed-preventers don’t work, or if you missed application. Follow the directions, but the post-emergent products are effective on very young crabgrass plants, such as before the four-leaf stage.
• Quackgrass can only be killed with products like glyphosate (Roundup and other brands), after it’s actively growing. There are no products that selectively remove quackgrass from lawns. Glyphosate can be spot-applied to quackgrass, which will also kill the lawngrass, making re-seeding necessary.

A third type of coarse, weedy grass that grows in dark green bunches is Tall Fescue. A perennial grass, control is the same as for quackgrass – spot spray with glyphosate (Roundup and others) followed by reseeding.

So when wide-bladed weedy grasses appear in our lawns, the very important first step is identification.

Happy Gardening, and may all your lawngrass be fine!